Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Kuusamonsali (Auditorium YB 210), Linnanmaa, on June 29th, 2000, at 12 noon.

Abstract

Water level regulation for purposes of hydropower production
has caused notable changes in the littoral zones of regulated lakes
in northern Finland. Marked geomorphological changes have taken place
in the lakes with a raised water level. Lowering of the ice cover
during the winter has also caused rapid changes in the littoral.
Changes in the environmental conditions and aquatic macrophyte communities
were studied largely by comparing the regulated Lake Ontojärvi
and the unregulated Lake Lentua in the Kainuu area. The general
aims of the study were to analyse environmental effects, to produce
information of ecological relationships for remedial measures on
the littoral and to apply the restoration methods in the management
of regulated lakes.

The most obvious effect of regulation was the expanded area
of extending ice, which caused an almost complete disappearance
of large ice-sensitive isoetids (Isoetes lacustris L., Lobelia dortmanna L.).
These species were largely replaced by small erosion resistant isoetids
(Ranunculus reptans L., Eleocharis
acicularis (L.) Roem. & Schult.). Another significant
change was the decreased frequency of large helophytes due to increased
erosion. A model based on environmental factors was able to predict
roughly the main vegetation types. Permanent plot studies showed
no significant differences in the stability of the vegetation between
the research lakes, which means that the species pool had adapted
to the harsh environment.

Restoration techniques based on mechanical protection of shorelines
and revegetation were applied to Lake Ontojärvi. The hostile
environmental conditions caused a rapid decline of the planted species,
but tall Salix phylicifolia L. seedlings and Carex
rostrata Stokes were able to survive, although in low
abundance. More significant remedial measures were provided by the
Ecologically-based Regulation Practices (ERP), which have been applied
to several lakes under hydropower production. This procedure, which
was largely based on the results of the Kainuu studies, offers a simple
way to illustrate the differences between various regulation practices.
Two case studies showed that an exceptional year with extremely
high or low water levels can largely abolish the positive succession
achieved by ERP. The huge financial losses caused by ERP for hydropower production
have also promoted the use of other conventional restoration measures.